This application claims the priority benefit of Taiwan application serial no. 88112203, filed Jul. 19, 1999.
1. Field of the Invention
This invention relates to a structure of a protective layer. More particularly, the invention relates to a structure of a multi-layered thin film protective layer of a reflective micro liquid crystal display (xcexc-LCD) device.
2. Description of the Related Art
The operation of a reflective micro-LCD device is based on application of a voltage to the metal layer on the surface of a control circuit. The electric field is generated to control the orientation of the liquid crystal. As light transmits through the liquid crystal and reaches the metal layer, the metal layer reflects the light, which in turn transmits through the liquid crystal. The different orientations of the liquid crystal display different optical properties, thereby displaying in different images on the reflective xcexc-LCD.
During the packaging of the reflective xcexc-LCD device, filling the liquid crystal requires coating a spacer between the glass plate and the device wafer to separate the glass plate and the device wafer. In addition, a protective layer is formed on the metal layer of the device surface to protect the underlying device.
The spacer, however, can only be coated on the periphery of the device, and the glass plate supported by the spacer bends easily at the center of the glass plate due to stress. As a result, while filling the liquid crystal, the thickness of the liquid crystal cannot be uniform. A Newton""s ring thus results. The non-uniform thickness of the liquid crystal seriously affects the quality of the display. Not only the displaying color is change, but the differentiation between the shades of color is also reduced.
The metal layer of the device requires a protective layer to prevent the metal surface from moisture penetration and from being scratched. The structure of the protective layer and the combination of thicknesses of the thin films directly affect the reflection property of the metal layer. The structure of the protective layer is therefore very critical for a reflective micro-LCD device.
In the light of the forgoing, the present invention provides protective layers of various structures to satisfy the needs of the different protective layers for the different device areas.
In addition, the present invention provides a protective layer structure as a spacer, which is located in the device wafer to support the glass plate and the device wafer and to improve the Newton""s ring effect.
The present invention also provides a structure of a multi-layered thin film protective layer, which is applicable to a substrate of a reflective micro-liquid crystal display, wherein the substrate includes a pixel cell area and a peripheral circuit area, and with each area comprising pixel cells and metal layer s, respectively. The structure of the multi-layered thin film protective layer includes a first protective layer formed in the peripheral circuit area and covering the metal layer and a plurality of pad spacers which are formed in the pixel cell area and the peripheral circuit area. The first protective layer includes a silicon nitride layer/oxide layer structure and the pad spacers include an oxide layer/silicon nitride layer/oxide layer structure, wherein the pad spacers are higher than the first protective layer. The structure of the multi-layered thin film protective layer further includes a second protective layer, formed in the pixel cell area covering the pixel cells, wherein the second protective layer includes a thin oxide layer.
The present invention accommodates the needs of different protective layers for the various device areas. A protective layer, which prevents moisture penetration and scratching, is formed to protect the device from being damaged. In the area that requires a high reflectivity, a protective layer with a high reflectivity is formed to fulfill the product requirement. In addition, pad spacers are formed on the device wafer, wherein the pad spacer is higher than the protective layer to facilitate the filling the liquid crystal and to lower the stress generated in packaging, thereby preventing the occurrence of the Newton""s ring effect. The thickness of the liquid crystal is therefore more uniform, and the resulting liquid crystal device has a better capability of differentiating the various shades of color.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.